Voltage regulators based on the energy band-gap voltage of a semiconductor material have been used in applications requiring temperature-stable operation. A band-gap voltage reference circuit provides a positive temperature coefficient (PTC) reference voltage, which when added to a negative temperature coefficient (NTC) reference voltage of proper magnitude, produces an overall reference voltage having a zero temperature coefficient (ZTC) characteristic. The PTC reference voltage is based on the emitter-base voltage differential (.DELTA.V.sub.BE) between a pair of current mirror transistors having different current densities. The NTC reference voltage is developed by the base-emitter voltages of one or more output transistors which operate to regulate a supply voltage at a level determined in relation to the overall reference voltage.
A shortcoming of the above-described ZTC voltage regulator is that the NTC reference voltage tends to vary with current density of the output transistors. This, in turn, varies the overall reference voltage, reducing the ability of the circuit to precisely regulate the supply voltage.